1. Field of the Invention
The present invention pertains to a support structure for offshore deepwater drilling and production platforms and the like characterized by a segmented filament wound composite support column connected to a gravity type base or anchor assembly.
2. Background
The continued development of offshore subsea wells for the recovery of hydrocarbon fluids has resulted in the encounter of several problems in the development of suitable structures for performing drilling and completion operations from above the surface of the sea and for producing fluids from the completed wells. The development of subsea production zones in waters 1000 feet deep or more has made it particularly desirable to consider the use of so-called fixed platform systems wherein a drilling or the sea on a structure which is fixed to or is resting on the sea bed. Although various types of deep water structural concepts have been considered, including guided towers, tension leg platforms and semi submersible vessel based floating platform systems, all of these concepts have certain disadvantages.
Many of the disadvantages of the aforementioned types of structures can be overcome with single or multiple, generally vertical column type structures which are adapted to be supported on the seabed and extend to or above the water surface. However, conventional construction techniques and engineering materials present certain problems for structures which may be required to be of a vertical height of from 1000 feet to as much as 3500 feet. For example, the foundation requirements for structures made solely of steel, concrete or combinations of both materials, are substantial and may require unreasonably large base structures to reduce the unit pressure on the seabed resulting from the weight of the column structure itself. With the latter supporting technique there is also always the possibility of the structure shifting or settling over a long period of time. Moreover, the problems associated with structural fatigue and corrosion using conventional engineering metals, the use of which has been previously thought necessary to make such a structure economically feasible, also appear to preclude the construction of so-called gravity base vertical column structures utilizing steel, for example, or reinforced concrete alone or in combination with each other.
It has been determined that there are several parameters which desirably should be satisfied when providing a deep water fixed platform structure of the type discussed herein. Primary considerations include the provision of a structure which is sufficiently stiff to withstand wave loads without incurring a list of more than about 8.degree. off horizontal. Moreover the structure should be able to withstand dynamic cyclic wind and wave induced loads and be resistant to fatigue failure caused by such loading. Such a structure should be resistant to corrosion caused by sea water and other environmental hazards and, of course, ease of fabrication must be considered to make the structure economically feasible. Although reinforced concrete structures have been given consideration with a view to satisfying the abovementioned criteria, such types of structures are not attractive from the standpoint of weight and fabrication or assembly requirements.
However, in pursuing the present invention, it has been determined that a structure supported on the seabed may be provided which is characterized by a single, segmented column assembly extending to or above the surface and which is fabricated primarily from a carbon or boron fiber-resin matrix having a tensile strength greater than and a modulus of elasticity approximately equal to or greater than alloy steel. Such a structure typically may have a density no more than 25% to 30% of that of a comparable steel structure. A deep water platform support structure is also contemplated in accordance with the present invention utilizing carbon, boron or a similar filament in a resin matrix to provide a composite shell disposed around a reinforced concrete cylinder which may serve as a mandrel on which the outer shell is constructed and is adapted to support particularly heavy static loads. The advantages and unique aspects of the present invention will be further evident to those skilled in the art upon reading the following summary and detailed description of the invention.